Apparatus and methods for additive manufacturing of three dimensional objects

ABSTRACT

A method of additive manufacturing a three-dimensional object by layerwise deposition of a building material with an inkjet printing system comprising a print head and a building tray, comprises calculating a weighting value for each nozzle, then for each layer obtaining a 2-D map of the layer, comprising active pixels at building material dispensing positions; obtaining a Data Correction Filter (DCF) including a height map of the previous layer, comparing the data of the 2D map to the data of the DCF at each position and determining if the nozzle at that position should dispense, then printing the layer, updating the weighting values and adjusting the position of the print head vis a vis the printing tray. The above is repeated until the three-dimensional object is printed.

RELATED APPLICATIONS

This application is a Continuation of PCT Patent Application No.PCT/IL2018/051399 having International filing date of Dec. 27, 2018,which claims the benefit of priority under USC § 119(e) of U.S.Provisional Patent Application No. 62/611,555 filed on Dec. 29, 2017.The contents of the above applications are all incorporated by referenceas if fully set forth herein in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to a methodand apparatus for minimizing the need for a roller in additivemanufacturing or 3D printing, and more particularly but not exclusively,to ways of depositing a layer in additive manufacturing to provide asmooth layer of consistent thickness.

A method of three-dimensional fabrication of an object is disclosed inU.S. Pat. No. 8,784,723 to the present Assignee. The method comprises:forming layers in a pattern corresponding to the shape of thethree-dimensional object, at least one layer of the plurality of layersbeing formed at a predetermined and different thickness selected so asto compensate for post-formation shrinkage of the layer along a verticaldirection. Spread of the layer building material of one or more layersis diluted at least locally such as to maintain a predeterminedthickness and a predetermined planar resolution for the layer.

A like issue is faced when increased resolution is needed. The increasedresolution requires increased nozzle usage and can have the unintendedconsequence of increasing layer thickness, and dilution may be employedto compensate for the increased thickness and produce a smoother, moreconsistent result. As stated therein, dilution is particularly usefulwhen it is desired to increase the resolution in the X direction. Thespread of building material per unit area is therefore diminished so asto compensate for any increment in the layer's thickness which may occuras a result of the increased resolution. The dismissing can be done bydiluting the spread of building material, by reducing the size ofdroplets, and the like.

The cited patent further discloses awareness of an additional problem,typically associated with types of printing apparatus which dispensebuilding materials through nozzle arrays, and which relates to theformation of defective locations on the layer. This problem is addressedby increasing the amount of building material in regions of thesubsequent layer which overlap the defective locations.

The citation teaches that the problems are solved by calculation inadvance and building a printing bitmap based on the expected layerthickness as predicted by the nozzles in operation. Then a dilutionratio is calculated and a new bitmap is constructed by applying adilution transformation based on modifying nozzle operation for thedilution ratio.

However, the modification is based on prior knowledge of the nozzles. Ifthe nozzles do not work as predicted, say some nozzles have been damagedor blocked since the previous calibration, or ink pressure has changedor for any other reason, then the advance calculation may not beaccurate, and a leveling device or planarizer (e.g. roller, scraper)must be relied upon to provide smoothness and/or desired thickness ofthe layer, with consequent raised levels of waste being generated.

Use of a roller for providing consistent smooth layers has a significantimpact on printer cost, reliability and waste production. Minimizing theneed for a roller or even eliminating its use would be useful and costefficient.

SUMMARY OF THE INVENTION

The present embodiments may compensate for non-uniformity in the printedlayer by measuring size of drops or droplets deposited from theindividual nozzles and using the droplet size to provide an estimate ofthe non-uniformity. The printing may then be modified to compensate. Theestimate may be made as a profile in the pre-print bit map.

Non-uniformities in the printed layers may be further be due todistribution and uneven size or layout of the printing nozzles in theprint head, and these features may further be used to modify thepre-print bit map. Compensation may involve modifying which nozzles areswitched on, and when.

Compensation may be carried out as above, that is based on nozzle dataknown in advance. Alternatively, compensation may be carried out basedon measurements of actual printed layer thickness obtained by scanningduring the printing process. Compensation may involve integrating thecorrection information into a filter referred to as a data correctionfilter (DCF).

In one embodiment, compensation is carried out initially based on nozzledata known in advance and then modified according to measurements takenin real time during the printing process.

It is noted that the compensation calculation carried out in advance maybe based on drop size and operational data of individual nozzles. Realtime modification may be based on actual layer thicknesses, as obtainedby surface scanning and the like, and combining the two requirescombining results of two different types of measurement.

The result may be a relatively flat layer at a known height, and thusthere is less flattening work for the roller to do. Thus, considerableresources are saved, as the roller in prior art systems typicallyremoves a large percentage of the material printed, leading toadditional cost, excessive use of printing material, waste removalissues with the printer, and environmental concerns, as well asincreasing the overall cost of the system and its maintenance.

According to an aspect of some embodiments of the present inventionthere is provided a method of additive manufacturing a three-dimensionalobject by layerwise deposition of a building material with an inkjetprinting system comprising a print head and a building tray, the methodcomprising:

calculating a weighting value for each nozzle of the printhead, theweighting value corresponding to an amount of material being dispensedby each of the nozzles;

for each layer of the object being printed:

obtaining a two-dimensional map of the layer, the two-dimensional mapcomprising active pixels at (X,Y) positions where building materialshould be dispensed;

obtaining a Data Correction Filter (DCF) including a height map of theprevious layer which comprises a series of (X,Y) position weightingvalues, each position weighting value being based on nozzle weightingvalues and representing the amount of material that has beencumulatively dispensed at each the (X,Y) position in the precedinglayers;

comparing the data of the two-dimensional map to the data of the DCF pereach (X,Y) position and determining if a nozzle should be activated atthe (X,Y) position to dispense an amount of material;

printing the layer based on the data obtained in (iii);

updating the position weighting values of the height map; and

adjusting the position of the print head vis a vis the printing tray.

This is followed by repeating steps (i) to (vi) above until thethree-dimensional object is printed.

In embodiments, the weighting value for each nozzle of the printhead iscalculated by: (a) pre-printing an object with a Y length of at leastthe length of the printhead, the object comprising a plurality of layersso that a print head printing profile can be observed; (b) digitizingthe pre-printed object and mapping each one the print head nozzles tothe profile; and (c) attributing a weighting value to each nozzle basedon the digitized printing profile.

In embodiments, the two-dimensional map of the layer of step (i) isprovided by a slicer software.

In embodiments, the DCF of step (ii) is stored in a computer memory.

In embodiments, the DCF further includes compensation data related toknown printing phenomena and/or to the geometry of the three-dimensionalobject being printed.

In embodiments, step (iii) comprises for each (X,Y) position: (a)determining if the pixel of the two-dimensional map is defined asactive; (b) determining if the position weighting value of the heightmap is equal or below a threshold value; and (c) if both (a) and (b) aretrue, activating the nozzle to dispense an amount of material at the(X,Y) position.

In embodiments, step (v) is performed by adding to each (X,Y) positionwherein a nozzle has been activated, the weighting value of the nozzleso that the (X,Y) position weighting value is updated.

Embodiments may comprise scanning the printed layer with a sensor andmodulating the DCF of the next layer with the data collected by thesensor.

In embodiments, the sensor is a CCD camera or a linear CCD camera.

In embodiments, the sensor is a proximity sensor.

Embodiments may comprise smoothing one or more printed layers with anyof a planarizer, a roller and a scraper.

In embodiments, the leveling device removes less than 5-10% of theamount of material deposited in the layer.

According to a second aspect of the invention there is provided a methodof additive manufacturing a three-dimensional object by layerwisedeposition of a building material with an inkjet printing systemcomprising a print head and a building tray, the method comprising foreach layer of the object being printed:

obtaining a two-dimensional map of the layer, the two-dimensional mapcomprising active pixels at (X,Y) positions where building materialshould be dispensed;

obtaining a Data Correction Filter (DCF) including a thickness mapand/or a proximity map of the previous layer; the map(s) beingconstructed from data obtained from one or more sensors that havescanned the previous layer;

comparing the data of the two-dimensional map to the data of the DCF pereach (X,Y) and determining if a nozzle should be activated at the (X,Y)position to dispense an amount of material;

printing the layer based on the data obtained in (iii); and

adjusting the position of the print head vis a vis the printing tray;

repeating steps (i) to (v) above until the three-dimensional object isprinted.

In embodiments, the DCF of step (ii) is stored in a computer memory.

In embodiments, step (iii) comprises for each (X,Y) position: (a)determining if the pixel of the two-dimensional map is defined asactive; (b) determining if the DCF value is equal or below a thresholdvalue; and (c) if both (a) and (b) are true, activating the nozzle todispense an amount of material at the (X,Y) position.

According to a third aspect of the present invention there is provided amethod of additive manufacturing a three-dimensional object by layerwisedeposition of a building material with an inkjet printing systemcomprising a print head and a building tray, the method comprising:

calculating a weighting value for each nozzle of the printhead, theweighting value corresponding to an amount of material being dispensedby each of the nozzles;

for each layer of the object being printed:

obtaining a two-dimensional map of the layer, the two-dimensional mapcomprising active pixels at (X,Y) positions where building materialshould be dispensed;

obtaining a first Data Correction Filter (DCF1) including a height mapof the previous layer which comprises a series of (X,Y) positionweighting values, each position weighting value being based on nozzleweighting values and representing the amount of material that has beencumulatively dispensed at each the (X,Y) position in the precedinglayers;

obtaining a second Data Correction Filter (DCF2) including a thicknessmap and/or a proximity map of the previous layer; the map(s) beingconstructed from data obtained from one or more sensors that havescanned the previous layer;

comparing the data of the two-dimensional map to the data provided byDCF1 and DCF2 per each (X,Y) position and determining whether a nozzleshould be activated at the (X,Y) position to dispense an amount ofmaterial;

printing the layer based on the data obtained in (iv);

updating the position weighting values of the height map of DCF1; and

adjusting the position of the print head vis a vis the printing tray;

repeating steps (i) to (vii) above until the three-dimensional object isprinted.

According to a fourth aspect of the present invention there may beprovided an inkjet additive manufacturing apparatus comprising a printhead, a building tray, a controller and a computing system suitable forperforming any of the above methods.

According to a further aspect of the present invention there is provideda method of additive manufacturing by depositing droplets of materialfrom a nozzle array of an inkjet print head to print a layer, the methodcomprising:

obtaining a thickness profile for a layer printed by a given print head,the thickness profile comprising irregularities;

using the thickness profile applying weightings to each of a pluralityof nozzles of the nozzle array;

using the nozzle weightings, generating a Data Correction Filter (DCF)to modify nozzle operation to compensate for irregularities in thethickness profile;

applying the DCF to incoming print data to produce modified print data;and

printing layers using the modified print data, thereby to produce layershaving actual profiles which are smoothed relative to the thicknessprofile.

The method may comprise refining the DCF based on variations in eitherof distribution and size within the plurality of nozzles.

The method may comprise inferring drop sizes from individual nozzles,and generating the nozzle weightings from the drop sizes.

The method may comprise activating individual pixels in a series toobtain the nozzle weightings.

In the method, the print data may comprise instructions for switchingrespective ones of the plurality of nozzles on and off over the courseof printing a layer.

In the method, the thickness profile may be modified based on printing atest layer and measuring thicknesses over the test layer.

The method may comprise scanning a last printed layer for an actuallayer thickness profile, and further modifying the DCF for a next layerto smooth the next layer in light of measured thicknesses in the actuallayer thickness profile.

In the method, the DCF may increase densities of operational nozzles inthin parts of the profile and decreases densities of operational nozzlesin thick parts of the profile.

According to a yet further aspect of the present invention there isprovided a method of additive manufacturing by depositing droplets ofmaterial from a nozzle array of an inkjet print head to print a layer,the method comprising:

scanning a currently printed layer;

determining a thickness profile of the currently printed layer from thescanning;

generating or modifying a DCF to modify nozzle operation to compensatefor irregularities in the thickness profile;

receiving print data;

applying the DCF to modify the print data; and

printing a new layer using the modified print data, thereby to producelayers having actual profiles which are smoothed relative to thethickness profile.

According to a third aspect of the present invention there is providedapparatus for additive manufacturing comprising:

an inkjet print head comprising a nozzle array comprising nozzles fordepositing droplets of material to print successive layers to form anobject;

a weighting device configured to deduce nozzle operation and drop sizefor a plurality of nozzles of the nozzle array and assign weightings tonozzles of the array;

a DCF unit configured to produce a transformation that modifies theweightings to smooth the layer profile, wherein the apparatus isconfigured to apply the DCF to printing plans to print a smooth layer.

According to a yet further aspect of the present invention there isprovided apparatus for additive manufacturing comprising:

an inkjet print head comprising a nozzle array comprising nozzles fordepositing droplets of material to print successive layers to form anobject;

a scanner for obtaining a profile of thicknesses of a printed layer;

a DCF unit associated with the scanner and configured to modifyweightings applied to the nozzles, the modification comprising weightingthe nozzles to cancel out irregularities in the profile and therebyproduce a smooth layer.

In an embodiment, the object is printed on a tray, the object being keptat a fixed distance from the nozzle array as new layers are added to theobject, and wherein the profile is fed back to regulate the objectheight.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a simplified diagram illustrating the use of a roller forsmoothing a layer after printing according to the known art;

FIGS. 2A-2C are simplified diagrams showing various problems that giverise to irregularities in the printed layer that require the use of aroller according to FIG. 1 ;

FIG. 3 is a simplified flow chart of the roller system according to theknown art;

FIG. 4A is a simplified flow chart illustrating a method of applyingpre-printing corrections to smooth a layer according to embodiments ofthe present invention;

FIG. 4B is a simplified flow chart illustrating a way of generating aDCF function for modifying operation of the nozzles according toembodiments of the present invention;

FIG. 5 is a simplified diagram illustrating an embodiment for real timecorrection of the nozzles based on scanning layer thicknesses accordingto the present invention;

FIG. 6 is a simplified diagram illustrating experimental data showingthe process of FIG. 4A;

FIG. 7 is a simplified flow chart showing a process for calibrating theDCF according to an embodiment of the present invention;

FIG. 8 is a simplified flow chart illustrating a procedural loop forcarrying out the process of FIG. 4A for multiple nozzles and printheads;

FIG. 9 is a simplified flow chart illustrating a procedural loop forcarrying out the process of FIG. 5 for multiple nozzles and print heads.

FIG. 10 is a simplified diagram showing how weightings applied to printnozzles may lead to a transfer function for printing a layer;

FIG. 11 is a simplified diagram showing in greater detail the embodimentof FIG. 4A;

FIG. 12 is a simplified diagram showing in greater detail the embodimentof FIG. 5 ;

FIG. 13 is a simplified diagram showing an embodiment that combines thefeatures of FIG. 4A and FIG. 5 ;

FIGS. 14A-D are schematic illustrations of an additive manufacturingsystem according to some embodiments of the invention;

FIGS. 15A-C are schematic illustrations of printing heads according tosome embodiments of the present invention; and

FIGS. 16A and 16B are schematic illustrations demonstrating coordinatetransformations according to some embodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to a methodand apparatus for minimizing the need for a leveling device orplanarizer (e.g. roller, scraper) in additive manufacturing or 3Dprinting and more particularly but not exclusively to ways of depositinga layer in additive manufacturing in a manner that provides smooth andconsistent layers.

A method of additive manufacturing according to the present embodimentsmay involve depositing droplets of material from a nozzle array of aninkjet print head to print a layer, and obtaining a thickness profilefor the layer as printed by a given print head. The thickness profile isgenerally not smooth but rather includes irregularities for reasonswhich are explained hereinbelow. The thickness profile is used to applyweightings to individual nozzles in the nozzle array. Then a DCFfunction is generated which modifies the weightings, and thus nozzleoperation, to compensate for the irregularities and thus generate asmoother profile. The DCF is used to modify incoming print data to printa layer with a smoother profile. The DCF may be based on pre-print data,or on real time scanning of the layer profile as printed or on acombination of both pre-printing and real time scanning data.

A method of additive manufacturing a three-dimensional object bylayerwise deposition of a building material with an inkjet printingsystem using a print head and a building tray, comprises calculating aweighting value for each nozzle, then for each layer obtaining a 2-D mapof the layer, comprising active pixels at building material dispensingpositions; obtaining a Data Correction Filter (DCF) including a heightmap of the previous layer, comparing the data of the 2D map to the dataof the DCF at each position and determining if the nozzle at thatposition should dispense, then printing the layer, updating theweighting values and adjusting the position of the print head vis a visthe printing tray. The above is repeated until the three-dimensionalobject is printed. The method and system of the present embodimentsmanufacture three-dimensional objects based on computer object data in alayerwise manner by forming a plurality of layers in a configuredpattern corresponding to the shape of the objects. The computer objectdata can be in any known format, including, without limitation, aStandard Tessellation Language (STL) or a StereoLithography Contour(SLC) format, Virtual Reality Modeling Language (VRML), AdditiveManufacturing File (AMF) format, Drawing Exchange Format (DXF), PolygonFile Format (PLY) or any other format suitable for Computer-Aided Design(CAD).

The term “object” as used herein refers to a whole object or a partthereof.

Each layer is formed by additive manufacturing apparatus which scans atwo-dimensional surface and patterns it. While scanning, the apparatusvisits a plurality of target locations on the two-dimensional layer orsurface, and decides, for each target location or a group of targetlocations, whether or not the target location or group of targetlocations is to be occupied by building material formulation, and whichtype of building material formulation is to be delivered thereto. Thedecision is made according to a computer image of the surface.

In preferred embodiments of the present invention the AM comprisesthree-dimensional printing, more preferably three-dimensional inkjetprinting. In these embodiments a building material formulation isdispensed from a dispensing head having a set of nozzles to depositbuilding material formulation in layers on a supporting structure. TheAM apparatus thus dispenses building material formulation in targetlocations which are to be occupied and leaves other target locationsvoid. The apparatus typically includes a plurality of dispensing heads,each of which can be configured to dispense a different buildingmaterial formulation. Thus, different target locations can be occupiedby different building material formulations. The types of buildingmaterial formulations can be categorized into two major categories:modeling material formulation and support material formulation. Thesupport material formulation serves as a supporting matrix orconstruction for supporting the object or object parts during thefabrication process and/or other purposes, e.g., providing hollow orporous objects. Support constructions may additionally include modelingmaterial formulation elements, e.g. for further support strength.

The modeling material formulation is generally a composition which isformulated for use in additive manufacturing and which is able to form athree-dimensional object on its own, i.e., without having to be mixed orcombined with any other substance.

The final three-dimensional object is made of the modeling materialformulation or a combination of modeling material formulations ormodeling and support material formulations or modification thereof(e.g., following curing). All these operations are well-known to thoseskilled in the art of solid freeform fabrication.

In some exemplary embodiments of the invention an object is manufacturedby dispensing two or more different modeling material formulations, eachmaterial formulation from a different dispensing head of the AM. Thematerial formulations are optionally and preferably deposited in layersduring the same pass of the printing heads. The material formulationsand combination of material formulations within the layer are selectedaccording to the desired properties of the object.

A representative and non-limiting example of a system 1110 suitable forAM of an object 1112 according to some embodiments of the presentinvention is illustrated in FIG. 14A. System 1110 comprises an additivemanufacturing apparatus 1114 having a dispensing unit 1016 whichcomprises a plurality of dispensing heads. Each head preferablycomprises an array of one or more nozzles 1122, as illustrated in FIGS.15A-C described below, through which a liquid building materialformulation 1124 is dispensed.

Preferably, but not obligatorily, apparatus 1114 is a three-dimensionalprinting apparatus, in which case the dispensing heads are printingheads, and the building material formulation is dispensed via inkjettechnology. This need not necessarily be the case, since, for someapplications, it may not be necessary for the additive manufacturingapparatus to employ three-dimensional printing techniques.Representative examples of additive manufacturing apparatus contemplatedaccording to various exemplary embodiments of the present inventioninclude, without limitation, fused deposition modeling apparatus andfused material formulation deposition apparatus.

Each dispensing head is optionally and preferably fed via a buildingmaterial formulation reservoir which may optionally include atemperature control unit (e.g., a temperature sensor and/or a heatingdevice), and a material formulation level sensor. To dispense thebuilding material formulation, a voltage signal is applied to thedispensing heads to selectively deposit droplets of material formulationvia the dispensing head nozzles, for example, as in piezoelectric inkjetprinting technology. The dispensing rate of each head depends on thenumber of nozzles, the type of nozzles and the applied voltage signalrate (frequency). Such dispensing heads are known to those skilled inthe art of solid freeform fabrication.

Preferably, but not obligatorily, the overall number of dispensingnozzles or nozzle arrays is selected such that half of the dispensingnozzles are designated to dispense support material formulation and halfof the dispensing nozzles are designated to dispense modeling materialformulation, i.e. the number of nozzles jetting modeling materialformulations is the same as the number of nozzles jetting supportmaterial formulation. In the representative example of FIG. 14A, fourdispensing heads 1016 a, 1016 b, 1016 c and 1016 d are illustrated. Eachof heads 1016 a, 1016 b, 1016 c and 1016 d has a nozzle array. In thisExample, heads 1016 a and 1016 b can be designated for modeling materialformulation/s and heads 1016 c and 1016 d can be designated for supportmaterial formulation. Thus, head 1016 a can dispense a first modelingmaterial formulation, head 1016 b can dispense a second modelingmaterial formulation and heads 1016 c and 1016 d can both dispensesupport material formulation. In an alternative embodiment, heads 1016 cand 1016 d, for example, may be combined in a single head having twonozzle arrays for depositing support material formulation. In somefurther embodiments, at least one of the printing heads can dispense atleast two distinct building materials via two distinct arrays of nozzles(e.g. one support material and one model material, or two distinctmodeling materials).

Yet it is to be understood that it is not intended to limit the scope ofthe present invention and that the number of modeling materialformulation depositing heads (modeling heads) and the number of supportmaterial formulation depositing heads (support heads) may differ.Generally, the number of modeling heads, the number of support heads andthe number of nozzles in each respective head or head array are selectedsuch as to provide a predetermined ratio, a, between the maximaldispensing rate of the support material formulation and the maximaldispensing rate of modeling material formulation. The value of thepredetermined ratio, a, is preferably selected to ensure that in eachformed layer, the height of modeling material formulation equals theheight of support material formulation. Typical values for a are fromabout 0.6 to about 1.5.

As used herein the term “about” refers to ±10%.

For example, for a=1, the overall dispensing rate of support materialformulation is generally the same as the overall dispensing rate of themodeling material formulation when all modeling heads and support headsoperate.

In a preferred embodiment, there are M modeling heads each having marrays of p nozzles, and S support heads each having s arrays of qnozzles such that M×m×p=S×s×q. Each of the M×m modeling arrays and S xssupport arrays can be manufactured as a separate physical unit, whichcan be assembled and disassembled from the group of arrays. In thisembodiment, each such array optionally and preferably comprises atemperature control unit and a material formulation level sensor of itsown, and receives an individually controlled voltage for its operation.

Apparatus 1114 can further comprise a solidifying device 1324 which caninclude any device configured to emit light, heat or the like that maycause the deposited material formulation to hardened. For example,solidifying device 1324 can comprise one or more radiation sources,which can be, for example, an ultraviolet or visible or infrared lamp,or other sources of electromagnetic radiation, or electron beam source,depending on the modeling material formulation being used. In someembodiments of the present invention, solidifying device 1324 serves forcuring or solidifying the modeling material formulation.

The dispensing head and radiation source are preferably mounted in aframe or block 1128 which is preferably operative to reciprocally moveover a tray 1360, which serves as the working surface. In someembodiments of the present invention the radiation sources are mountedin the block such that they follow in the wake of the dispensing headsto at least partially cure or solidify the material formulations justdispensed by the dispensing heads. Tray 1360 is positioned horizontally.According to the common conventions an X-Y-Z Cartesian coordinate systemis selected such that the X-Y plane is parallel to tray 1360. Tray 1360is preferably configured to move vertically (along the Z direction),typically downward. In various exemplary embodiments of the invention,apparatus 1114 further comprises one or more leveling devices orplanarizer 1132, e.g. including a roller 1326. Leveling device 1132serves to straighten, level and/or establish a thickness of the newlyformed layer prior to the formation of the successive layer thereon.Leveling device 1132 preferably comprises a waste collection device 1136for collecting the excess material formulation generated duringleveling. Waste collection device 1136 may comprise any mechanism thatdelivers the material formulation to a waste tank or waste cartridge.

In use, the dispensing heads of unit 1016 move in a scanning direction,which is referred to herein as the X direction, and selectively dispensebuilding material formulation in a predetermined configuration in thecourse of their passage over tray 1360. The building materialformulation typically comprises one or more types of support materialformulation and one or more types of modeling material formulation. Thepassage of the dispensing heads of unit 1016 is followed by the curingof the modeling material formulation(s) by radiation source 1126. In thereverse passage of the heads, back to their starting point for the layerjust deposited, an additional dispensing of building materialformulation may be carried out, according to predeterminedconfiguration. In the forward and/or reverse passages of the dispensingheads, the layer thus formed may be straightened by leveling device1326, which preferably follows the path of the dispensing heads in theirforward and/or reverse movement. Once the dispensing heads return totheir starting point along the X direction, they may move to anotherposition along an indexing direction, referred to herein as the Ydirection, and continue to build the same layer by reciprocal movementalong the X direction. Alternately, the dispensing heads may move in theY direction between forward and reverse movements or after more than oneforward-reverse movement. The series of scans performed by thedispensing heads to complete a single layer is referred to herein as asingle scan cycle.

Once the layer is completed, tray 1360 is lowered in the Z direction toa predetermined Z level, according to the desired thickness of the layersubsequently to be printed. The procedure is repeated to formthree-dimensional object 1112 in a layerwise manner.

In another embodiment, tray 1360 may be displaced in the Z directionbetween forward and reverse passages of the dispensing head of unit1016, within the layer. Such Z displacement is carried out in order tocause contact of the leveling device with the surface in one directionand prevent contact in the other direction.

System 1110 optionally and preferably comprises a building materialformulation supply system 1330 which comprises the building materialformulation containers or cartridges and supplies a plurality ofbuilding material formulations to fabrication apparatus 1114.

A control unit 1340 controls fabrication apparatus 1114 and optionallyand preferably also supply system 1330. Control unit 1340 typicallyincludes an electronic circuit configured to perform the controllingoperations. Control unit 1340 preferably communicates with a dataprocessor 1154 which transmits digital data pertaining to fabricationinstructions based on computer object data, e.g., a CAD configurationrepresented on a computer readable medium in a form of a StandardTessellation Language (STL) format or the like. Typically, control unit1340 controls the voltage applied to each dispensing head or nozzlearray and the temperature of the building material formulation in therespective printing head.

Once the manufacturing data is loaded to control unit 1340 it canoperate without user intervention. In some embodiments, control unit1340 receives additional input from the operator, e.g., using dataprocessor 1154 or using a user interface 1116 communicating with unit1340. User interface 1116 can be of any type known in the art, such as,but not limited to, a keyboard, a touch screen and the like. Forexample, control unit 1340 can receive, as additional input, one or morebuilding material formulation types and/or attributes, such as, but notlimited to, color, characteristic distortion and/or transitiontemperature, viscosity, electrical property, magnetic property. Otherattributes and groups of attributes are also contemplated.

Another representative and non-limiting example of a system 1010suitable for AM of an object according to some embodiments of thepresent invention is illustrated in FIGS. 14B-D. FIGS. 14B-D illustratea top view (FIG. 14B), a side view (FIG. 14C) and an isometric view(FIG. 14D) of system 1010.

In the present embodiments, system 1010 comprises a tray 1012 and aplurality of inkjet printing heads 1016, each having a plurality ofseparated nozzles. Tray 1012 can have a shape of a disk or it can beannular. Non-round shapes are also contemplated, provided they can berotated about a vertical axis.

Tray 1012 and heads 1016 are optionally and preferably mounted such asto allow a relative rotary motion between tray 1012 and heads 1016. Thiscan be achieved by (i) configuring tray 1012 to rotate about a verticalaxis 1014 relative to heads 1016, (ii) configuring heads 1016 to rotateabout vertical axis 1014 relative to tray 1012, or (iii) configuringboth tray 1012 and heads 1016 to rotate about vertical axis 1014 but atdifferent rotation velocities (e.g., rotation at opposite direction).While the embodiments below are described with a particular emphasis toconfiguration (i) wherein the tray is a rotary tray that is configuredto rotate about vertical axis 1014 relative to heads 1016, it is to beunderstood that the present application contemplates also configurations(ii) and (iii). Any one of the embodiments described herein can beadjusted to be applicable to any of configurations (ii) and (iii), andone of ordinary skills in the art, provided with the details describedherein, would know how to make such adjustment.

In the following description, a direction parallel to tray 1012 andpointing outwardly from axis 1014 is referred to as the radial directionr, a direction parallel to tray 1012 and perpendicular to the radialdirection r is referred to herein as the azimuthal direction φ, and adirection perpendicular to tray 1012 is referred to herein is thevertical direction z.

The term “radial position,” as used herein, refers to a position on orabove tray 1012 at a specific distance from axis 1014. When the term isused in connection to a printing head, the term refers to a position ofthe head which is at specific distance from axis 1014. When the term isused in connection to a point on tray 1012, the term corresponds to anypoint that belongs to a locus of points that is a circle whose radius isthe specific distance from axis 1014 and whose center is at axis 1014.

The term “azimuthal position,” as used herein, refers to a position onor above tray 1012 at a specific azimuthal angle relative to apredetermined reference point. Thus, radial position refers to any pointthat belongs to a locus of points that is a straight line forming thespecific azimuthal angle relative to the reference point.

The term “vertical position,” as used herein, refers to a position overa plane that intersect the vertical axis 1014 at a specific point.

Tray 1012 serves as a supporting structure for three-dimensionalprinting. The working area on which one or objects are printed istypically, but not necessarily, smaller than the total area of tray1012. In some embodiments of the present invention the working area isannular. The working area is shown at 1026. In some embodiments of thepresent invention tray 1012 rotates continuously in the same directionthroughout the formation of object, and in some embodiments of thepresent invention tray reverses the direction of rotation at least once(e.g., in an oscillatory manner) during the formation of the object.Tray 1012 is optionally and preferably removable. Removing tray 1012 canbe for maintenance of system 1010, or, if desired, for replacing thetray before printing a new object. In some embodiments of the presentinvention system 1010 is provided with one or more different replacementtrays (e.g., a kit of replacement trays), wherein two or more trays aredesignated for different types of objects (e.g., different weights)different operation modes (e.g., different rotation speeds), etc. Thereplacement of tray 1012 can be manual or automatic, as desired. Whenautomatic replacement is employed, system 1010 comprises a trayreplacement device 1036 configured for removing tray 1012 from itsposition below heads 1016 and replacing it by a replacement tray (notshown). In the representative illustration of FIG. 14B tray replacementdevice 1036 is illustrated as a drive 1038 with a movable arm 1040configured to pull tray 1012, but other types of tray replacementdevices are also contemplated.

Exemplified embodiments for the printing head 1016 are illustrated inFIGS. 15A-15C. These embodiments can be employed for any of the AMsystems described above, including, without limitation, system 1110 andsystem 1010.

FIGS. 15A-B illustrate a printing head 1016 with one (FIG. 15A) and two(FIG. 15B) nozzle arrays 1022. The nozzles in the array are preferablyaligned linearly, along a straight line. In embodiments in which aparticular printing head has two or more linear nozzle arrays, thenozzle arrays are optionally and preferably can be parallel to eachother.

When a system similar to system 1110 is employed, all printing heads1016 are optionally and preferably oriented along the indexing directionwith their positions along the scanning direction being offset to oneanother.

When a system similar to system 1010 is employed, all printing heads1016 are optionally and preferably oriented radially (parallel to theradial direction) with their azimuthal positions being offset to oneanother. Thus, in these embodiments, the nozzle arrays of differentprinting heads are not parallel to each other but are rather at an angleto each other, which angle being approximately equal to the azimuthaloffset between the respective heads. For example, one head can beoriented radially and positioned at azimuthal position φ₁, and anotherhead can be oriented radially and positioned at azimuthal position φ₂.In this example, the azimuthal offset between the two heads is φ₁-φ₂,and the angle between the linear nozzle arrays of the two heads is alsoφ₁-φ₂.

In some embodiments, two or more printing heads can be assembled to ablock of printing heads, in which case the printing heads of the blockare typically parallel to each other. A block including several inkjetprinting heads 1016 a, 1016 b, 1016 c is illustrated in FIG. 15C.

In some embodiments, system 1010 comprises a stabilizing structure 1030positioned below heads 1016 such that tray 1012 is between stabilizingstructure 1030 and heads 1016. stabilizing structure 1030 may serve forpreventing or reducing vibrations of tray 1012 that may occur whileinkjet printing heads 1016 operate. In configurations in which printingheads 1016 rotate about axis 1014, stabilizing structure 1030 preferablyalso rotates such that stabilizing structure 1030 is always directlybelow heads 1016 (with tray 1012 between heads 1016 and tray 1012).

Tray 1012 and/or printing heads 1016 are optionally and preferablyconfigured to move along the vertical direction z, parallel to verticalaxis 1014 so as to vary the vertical distance between tray 1012 andprinting heads 1016. In configurations in which the vertical distance isvaried by moving tray 1012 along the vertical direction, stabilizingstructure 1030 preferably also moves vertically together with tray 1012.In configurations in which the vertical distance is varied by heads 1016along the vertical direction, while maintaining the vertical position oftray 1012 fixed, support stabilizing 1030 is also maintained at a fixedvertical position.

The vertical motion can be established by a vertical drive 1028. Once alayer is completed, the vertical distance between tray 1012 and heads1016 can be increased (e.g., tray 1012 is lowered relative to heads1016) by a predetermined vertical step, according to the desiredthickness of the layer subsequently to be printed. The procedure isrepeated to form a three-dimensional object in a layerwise manner.

The operation of inkjet printing heads 1016 and optionally andpreferably also of one or more other components of system 1010, e.g.,the motion of tray 1012, are controlled by a controller 1020. Thecontroller can have an electronic circuit and a non-volatile memorymedium readable by the circuit, wherein the memory medium stores programinstructions which, when read by the circuit, cause the circuit toperform control operations as further detailed below.

Controller 1020 can also communicate with a host computer 1024 whichtransmits digital data pertaining to fabrication instructions based oncomputer object data, e.g., in a form of a Standard TessellationLanguage (STL) or a StereoLithography Contour (SLC) format, VirtualReality Modeling Language (VRML), Additive Manufacturing File (AMF)format, Drawing Exchange Format (DXF), Polygon File Format (PLY) or anyother format suitable for Computer-Aided Design (CAD). The object dataformats are typically structured according to a Cartesian system ofcoordinates. In these cases, computer 1024 preferably executes aprocedure for transforming the coordinates of each slice in the computerobject data from a Cartesian system of coordinates into a polar systemof coordinates. Computer 1024 optionally and preferably transmits thefabrication instructions in terms of the transformed system ofcoordinates. Alternatively, computer 1024 can transmit the fabricationinstructions in terms of the original system of coordinates as providedby the computer object data, in which case the transformation ofcoordinates is executed by the circuit of controller 1020.

The transformation of coordinates allows three-dimensional printing overa rotating tray. In conventional three-dimensional printing, theprinting heads reciprocally move above a stationary tray along straightlines. In such conventional systems, the printing resolution is the sameat any point over the tray, provided the dispensing rates of the headsare uniform. Unlike conventional three-dimensional printing, not all thenozzles of the head points cover the same distance over tray 1012 duringat the same time. The transformation of coordinates is optionally andpreferably executed so as to ensure equal amounts of excess materialformulation at different radial positions. Representative examples ofcoordinate transformations according to some embodiments of the presentinvention are provided in FIGS. 16A-B, showing three slices of an object(each slice corresponds to fabrication instructions of a different layerof the objects), where FIG. 16A illustrates a slice in a Cartesiansystem of coordinates and FIG. 16B illustrates the same slice followingan application of a transformation of coordinates procedure to therespective slice.

Typically, controller 1020 controls the voltage applied to therespective component of the system 1010 based on the fabricationinstructions and based on the stored program instructions as describedbelow.

Generally, controller 1020 controls printing heads 1016 to dispense,during the rotation of tray 1012, droplets of building materialformulation in layers, such as to print a three-dimensional object ontray 1012.

System 1010 optionally and preferably comprises one or more radiationsources 1018, which can be, for example, an ultraviolet or visible orinfrared lamp, or other sources of electromagnetic radiation, orelectron beam source, depending on the modeling material formulationbeing used. Radiation source can include any type of radiation emittingdevice, including, without limitation, light emitting diode (LED),digital light processing (DLP) system, resistive lamp and the like.Radiation source 1018 serves for curing or solidifying the modelingmaterial formulation. In various exemplary embodiments of the inventionthe operation of radiation source 1018 is controlled by controller 1020which may activate and deactivate radiation source 1018 and mayoptionally also control the amount of radiation generated by radiationsource 1018.

In some embodiments of the invention, system 1010 further comprises oneor more leveling devices 1032 which can be manufactured as a roller or ablade. Leveling device 1032 serves to straighten the newly formed layerprior to the formation of the successive layer thereon. In someembodiments, leveling device 1032 has the shape of a conical rollerpositioned such that its symmetry axis 1034 is tilted relative to thesurface of tray 1012 and its surface is parallel to the surface of thetray. This embodiment is illustrated in the side view of system 1010(FIG. 14C).

The conical roller can have the shape of a cone or a conical frustum.

The opening angle of the conical roller is preferably selected such thatis a constant ratio between the radius of the cone at any location alongits axis 1034 and the distance between that location and axis 1014. Thisembodiment allows roller 1032 to efficiently level the layers, sincewhile the roller rotates, any point p on the surface of the roller has alinear velocity which is proportional (e.g., the same) to the linearvelocity of the tray at a point vertically beneath point p. In someembodiments, the roller has a shape of a conical frustum having a heighth, a radius R₁ at its closest distance from axis 1014, and a radius R₂at its farthest distance from axis 1014, wherein the parameters h, R₁and R₂ satisfy the relation R₁/R₂=(R−h)/h and wherein R is the farthestdistance of the roller from axis 1014 (for example, R can be the radiusof tray 1012).

The operation of leveling device 1032 is optionally and preferablycontrolled by controller 1020 which may activate and deactivate levelingdevice 1032 and may optionally also control its position along avertical direction (parallel to axis 1014) and/or a radial direction(parallel to tray 1012 and pointing toward or away from axis 1014.

In some embodiments of the present invention printing heads 1016 areconfigured to reciprocally move relative to tray along the radialdirection r. These embodiments are useful when the lengths of the nozzlearrays 1022 of heads 1016 are shorter than the width along the radialdirection of the working area 1026 on tray 1012. The motion of heads1016 along the radial direction is optionally and preferably controlledby controller 1020.

Some embodiments contemplate the fabrication of an object by dispensingdifferent material formulations from different dispensing heads. Theseembodiments provide, inter alia, the ability to select materialformulations from a given number of material formulations and definedesired combinations of the selected material formulations and theirproperties. According to the present embodiments, the spatial locationsof the deposition of each material formulation with the layer isdefined, either to effect occupation of different three-dimensionalspatial locations by different material formulations, or to effectoccupation of substantially the same three-dimensional location oradjacent three-dimensional locations by two or more different materialformulations so as to allow post deposition spatial combination of thematerial formulations within the layer, thereby to form a compositematerial formulation at the respective location or locations.

Any post deposition combination or mix of modeling material formulationsis contemplated. For example, once a certain material formulation isdispensed it may preserve its original properties. However, when it isdispensed simultaneously with another modeling material formulation orother dispensed material formulations which are dispensed at the same ornearby locations, a composite material formulation having a differentproperty or properties to the dispensed material formulations is formed.

The present embodiments thus enable the deposition of a broad range ofmaterial formulation combinations, and the fabrication of an objectwhich may consist of multiple different combinations of materialformulations, in different parts of the object, according to theproperties desired to characterize each part of the object.

Further details on the principles and operations of an AM systemsuitable for the present embodiments are found in U.S. PublishedApplication No. 20100191360, the contents of which are herebyincorporated by reference.

For purposes of better understanding some embodiments of the presentinvention, as illustrated in FIGS. 4A-13 of the drawings, reference isfirst made to the construction and operation of conventionalroller-based flattening as illustrated in FIG. 1 , and to issues arisingtherewith that have come to the attention of the present inventors, asshown in FIGS. 2A-2C and 3 .

As illustrated in FIG. 1 , print head block 10 deposits new layer 12over previously deposited layer 14. Due to various factors which arediscussed herein, the newly deposited layer has a relatively roughsurface 16. In order to obtain a smooth surface and control layerthickness, roller 18 is used for leveling the newly deposited layer,thereby removing a portion of the material freshly deposited (see A).The result is a smooth surface 20 after the passage of the roller, but asubstantial amount of material deposited for building layer 12 has beenremoved. Besides flattening the surface, the roller is used to remove apre-determined amount of material to maintain a fixed distance betweenthe print head block and each of the printed layers. Arrow B shows thefixed distance between the print head block and the intended layersurface (equivalent to surface 20) after the passage of roller 18.

FIGS. 2A-2C illustrate some of the problems that may occur in inkjetadditive manufacturing. FIG. 2A illustrates the issue of crosstalk. Amodel 30 is printed on tray 32. Material peaks at 34 and 36 causedistortion effects known as crosstalk, and when using a roller may causeknocking of the roller on the material peaks.

FIG. 2B illustrates two different materials 40 and 42 printed next toeach other, for example a model material with a support material. Awetting interaction distorts the shape 44 at the junction between them.

FIG. 2C shows a side view of a block 46 formed by dispensing severallayers of building material without indexing the dispensing head in theY direction. An uneven surface can be seen, which may be due to one ormore defects in the printing head, such as irregularities in nozzlesize, distance accuracy between consecutive nozzles in the nozzle array,or differences in jetting power between the nozzles.

Reference is now made to FIG. 3 , which is a block diagram of a 3Dprinter using a roller according to FIG. 1 . The printing tray thatholds the object being printed is moved down at the end of each layer bythe width of the layer to be added, based on thickness value 50 (e.g. 30μm). Roller 54 removes excess material from the newly printed layer(e.g. any material above the 30 μm pre-determined thickness), which mayadd up to 20-30% of the amount of material deposited. Then slicer data56 is supplied as input to print a new layer 58, and the tray is moveddown again and the new layer is leveled.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

Pre-print data correction at the level of slicer bitmaps can handleeffects that are predictable or partially predictable, such as crosstalk, lack of uniformity between nozzle drop volumes of differentnozzles, and so on, before the printing procedure commences.

Reference is now made to FIG. 4A, which is a simplified flow chartillustrating a method of providing a printed layer which is smooth orsubstantially smooth from the outset according to one embodiment of thepresent invention. The method involves a pre-printing or calibrationstage 60 and a printing stage 62. Pre-printing stage 60 includesobtaining nozzle “weightings” corresponding to the “jetting power” ofeach individual nozzles of the print head. For this purpose, a digitizedhead profile may be obtained by printing an object (e.g. a wall) havinga length of at least the length of the printhead array, said objectbeing printed by depositing several layers of materials without using aleveling device (e.g. roller) and without moving the printhead in the Ydirection. The whole object or a side/Y cross-section is then capturedvia a digital means (e.g. digital camera or digital scanner) to generatea digitized profile corresponding to the printing output of a specificprint head (box 64). Then, the position of each individual nozzle of theprint head is mapped on its digitized profile (box 66). Nozzles mappingis then used to give the nozzles individual weightings (box 68), whichis related to the drop size produced by that nozzle.

Based on the weightings, a data correction filter (hereafter alsoreferred as “DCF”) is then generated (box 70) which increases operation(e.g. at the level of the slicer data) around thin parts of the profile,e.g. by addition of material, optionally by adding slices of material,where the printed surface is liable to be lower or less than the desiredlayer height, and decreases operation around thicker parts of theprofile, e.g. by dilution where the printed surface is liable to beabove the desired layer height, so as to provide a smoother layersurface at a consistent height. The DCF is in a sense an inversefunction of the thickness profile.

Generation of the DCF is discussed in further detail in FIG. 4B below.

In printing stage 62, printing data is received from the slicer in theform of a 2D layer map that defines which pixel of the layer is“activated” (deposition of material at this specific (X,Y) coordinate),and which one is not. The 2D layer map received from the slicer is thenmodified using the DCF, and the modified print data is used to operatethe print head during the printing of the layer, thereby obtaining asmooth layer with a minimal intervention of the leveling device (e.g.roller). In some specific embodiments of the invention, no levelingdevice is used. Thanks to the present invention, the roller hasconsiderably less smoothing to do and far less material is removed, forinstance between 0-20%, or between 1-10%, or less than 5% of the totalamount of material deposited to form a specific layer. In specificembodiments, no roller is needed at all.

The nozzle weightings and the DCF may relate to individual drop sizesfrom given nozzles. The position weightings, which corresponds forinstance to a specific position on the data provided to print a specificslide, e.g. a pixel on a 2D map, may take into account the nozzleweightings of the nearby nozzles that influence the given position, thestrength of the jet from the individual nozzle above said givenposition, and optionally any further irregularities related to nozzlepositioning on the print head.

The print data comprises instructions for activating or inactivatingnozzles over the course of print head scanning for printing a layer orpart of a layer, and the DCF modifies the operation of individualnozzles, typically by providing a multiplier to the given nozzle. Asshown above, nozzles individual weighting may be obtained based onmeasurements made on a test or calibration layer.

Reference is now made to FIG. 4B, which shows a method for generation ofthe DCF in greater detail. As shown in FIG. 4A, a digitized head profileis obtained (box 64), the position of each individual nozzle of theprint head is mapped (box 66), and individual weighting is attributed toeach one of the nozzles (box 68). Nozzles mapping is then used to givethe nozzles individual weightings 68, which may correspond to the dropsize produced by that nozzle.

During the printing process, for each (X,Y) position or coordinate ofthe object being printed (box 72), the overall thickness is calculatedby summing up the respective weightings of the jetting nozzles that haveprinted the previous slices at the same (X,Y) position (box 74). Athickness value at said (X,Y) position (or “position weighting”) isobtained (box 76). If taken together, the position weightings at each(X,Y) position form a height map as exemplified in FIG. 10 . This heightmap is generally different on a per layer basis, since the positionweighting values will be higher if more layers have been printed.

Reference is now made to FIG. 5 , which illustrates a further embodimentof the invention in which the printing process can rely on a real-timefeedback loop, the thickness data being provided by one or more sensorsinstalled in the printing system. This embodiment may be usedindependently from the embodiment described in FIG. 4A, in which case aninitial DCF is obtained from a first scanned printed layer.

In FIG. 5 , an earlier layer (Z=n−1) is printed (box 80). This layer isscanned after printing to obtain an actual thickness profile, gatheringdata for each (X,Y) position of the layer (box 82). The actual thicknessis then used to ensure that the distance between the print head(s) andthe new layer to be printed is kept constant. If the distance is notappropriate, the Z-height of the tray (or of the print head/printingblock) may be corrected (box 84). The actual thickness may also be usedto modify the DCF (box 86), so that the DCF may take into accountdynamic changes occurring during the course of printing, for instance anozzle becoming blocked. Finally, a new layer is printed (Z=n) (box 88).

As discussed above, the DCF may be a function that operates on incomingprint data to increase densities of operational nozzles in thin parts ofthe layer profile and decreases densities of operational nozzles inthick parts of the profile.

The scan may be carried out using a laser scanner, or any othermeasurement device that may quickly and conveniently provide a thicknessprofile for the layer.

Reference is now made to FIG. 6 , which illustrates various stages ofthe process of FIG. 4A using images obtained from a test operation.Several layers are printed to form a bar or wall in order to obtain athickness profile of the print head. Head profile 90, which is a Z/Yside view of the printed bar, shows variations of height due todifference in the amount of material deposited by each one of the headnozzles.

The profile is then digitized and may be used to produce graph 92. Basedon graph 92, weightings can be assigned to the different nozzles of thenozzle head. The nozzle weightings can for example be estimates of thedrop size or amount of material jetted by the nozzle. The nozzleweighting value can be further modified based on known irregularities ofthe nozzle layout and the like, or one can consider that theseirregularities are taken into account in the nozzle weighting value.

A data dilution plan or Data Correction Filter (DCF) 94 is then preparedwhich is in a sense the negative or inverse function of the thicknessprofile. When applied to incoming print data (e.g. 2D layer map providedby the slicing software), applying the DCF before printing the layerhelped obtaining a smooth profile as shown in 96. It is apparent fromthe picture that the profile is not 100% smooth and still has some bumpsand hollows, but profile 96 is nevertheless far smoother than profile 90generated without correction. Then, a leveling device may be applied toremove between 0-20% of the material a further smooth the layer.

The pre-print data correction when used alone may reduce phenomenarelating to material placement but relies on a forecast of all phenomenathat may occur. The use of real time correction during printing addsfeedback on the distance from the print head, as well as feedback onmissing or bad nozzles. However, the real-time correction requiresscanning, which can decrease throughput, and therefore in embodiments,the real-time correction is preferably applied at preset intervals andnot at every layer. A real-time correction requires the addition of amodule that can scan the entire printed surface of an object.

A second or additional approach to data correction involves datacorrection while i.e. during the course of printing, e.g. by using asensor. Use of a sensor enables to manipulate the printed data as afunction of real printing results, depending on the type of sensor used.For example, a 1D sensor can be used to monitor the distance of theorifice plate on which the nozzles are mounted, from the printingsurface, A 2D sensor may monitor variations in height of a wall formedduring printing, The variation in wall height provides real-timefeedback about the surface of a model being printed, such as a virtualheight map of the printed model, e.g. based on the data obtainedregarding which nozzle is depositing material and where, as well as thedrop volume of each nozzle. A 3D sensor would monitor surface heightvariation of the entire printed surface of the object being printed.

Optionally, a combination of pre-print data correction and datacorrection during printing may be employed.

Reference is now made to FIG. 7 , which is a simplified flow chartillustrating an embodiment of the printing process of the invention. Theprinting system calculates or provide a height map (or tray map)previously stored, which represents accumulated data of the previouslyprinted layers (see FIG. 4B). The Height Map of layer n−1 is initializedbefore printing new layer n (box 100). For each scanning position of thehead, a test is performed for each one of its nozzles to determinewhether material should be jetted by the nozzle or not. In the presentexample, nozzle 1 of head 1 is located at a (X,Y) position(corresponding to a specific pixel of a 2D layer map or slice) and isbeing tested (box 102). First, the 2D layer map corresponding to layer nis interrogated to determine whether the pixel at (X,Y) position is“active” or not, i.e. whether material is planned to be deposited or notat this location according to the 2D layer map provided by the slicer(box 104). If the pixel has been set as “active”, then the (X,Y)position is tested to determine whether the position weighting value atthis location of the height map is above or below a pre-determinedthreshold (box 106). This threshold value may typically be related tothe number of drops that have been deposited at this location and thetheoretical thickness provided by each individual drop. If the positionweighting is equal or below to the pre-determined threshold value, thenozzle is activated, a drop of material is deposited at location (X,Y),and the nozzle weighting value is added at the (X,Y) location positionweighting value of the height map (box 108). The next nozzle of the headis selected (box 110) and testing is repeated until all thenozzles/positions have been checked. At box 112 the loop checks for thelast nozzle. If the tested nozzle was not the last nozzle of the head,then the loop is repeated and if not then the next print head isselected (box 114) and the process is repeated for the following head,unless this is detected to be the final head (box 116) in which case thepass number is incremented (box 118). Box 120 checks if the pass numberis the last pass and if so the process is ended.

Reference is now made to FIG. 8 , which is a simplified flow chartshowing an embodiment in which the calibrations, here denoted the scanreference block, are used to print a subsequent layer. The processdistinguishes between odd and even passes in 130. In even passes at 132the scan reference block is consulted and the nozzle is modifiedaccording to the calibration during processing of print data in 134. In136 the layer is printed and in 138 the process loops round for the nextlayer or exits to 140.

Reference is now made to FIG. 9 , which is a simplified flow diagramshowing how the real-time corrections may be carried out. The print datais obtained in 148 and the scan is initiated with line 0 in 150. At 152the line is scanned to see if it is above threshold or not. If the scanis above threshold then in 154 the nozzles for the line are switchedoff. Otherwise printing proceeds accordingly. In 156 the line isincremented and the process loops until the final line is identified in158 and the process exits at 160.

Reference is now made to FIG. 10 which shows a print heads PH-1 170having a linear array of ten nozzles. Weightings are assigned to each ofthe nozzles, for instance, based on the data extracted from a digitizedhead profile (see FIG. 4A). A height map 176 can be built during theprinting process, in which cumulative position weightings information isstored. Each square of the height map represents a specific (X,Y)coordinate. When a value appears in a specific square, it means that atleast one drop of material has been deposited at this location whenprinting at least one of the preceding layers (i.e. the pixel has beendefined as “active” in at least one of the 2D layer map/slice). When novalue appears in the square, it means that no material has been printedat this location so far. Each time a drop is jetted by a specific nozzleat a specific position, the nozzle weighting is added to the existingvalue in the corresponding location of the height map. In the presentcase, height map 176 represents two scans of print head 170. Anotherpossible representation of the height map as used in the presentinvention is shown in 178.

Reference is now made to FIG. 11 , which is a block diagram showing aprinting process which includes a pre-printing calibration stepaccording to some embodiments of the invention. Pre-print data includesprint heads nozzles weighting information 180 as shown in FIG. 10 , andmay also include other information/data relating to known printingphenomena 182, such as elevated contours (see FIG. 2A), wettinginteraction between resins (see FIG. 2B), thin wall, and any otherpredictable phenomenon related to the geometry of the object to beprinted. Print data from slicing 184, typically a 2D layer map, (e.g.BMP) is then combined with the pre-print data to form a correctionalgorithm filter 186 to be applied to the layer being printed 188.Finally, a subsequent layer 190 is printed.

Reference is now made to FIG. 12 , which is a simplified block diagramshowing real-time correction according to some embodiments of theinvention. Sensor 200 measures the actual thickness of a printed layer(output layer) and a comparator compares the result with print—orslice—data from slicer 184. Data correction algorithm filter 202 carriesout a transformation of the print data based on the measured errors sothat the printed layer 188 is smoothed. Movement of the tray isperformed and a subsequent layer 190 may be printed.

Reference is now made to FIG. 13 , which is a simplified block diagramshowing a combination of the embodiments shown of FIGS. 11 and 12 inwhich both pre-printing calibration and real-time correction are carriedout in the same printing process. Pre-print data is prepared from nozzleweighting distribution information 180 as discussed in FIG. 10 , and mayalso include other information/data relating to known printing phenomena182, such as elevated contours (see FIG. 2A), wetting interactionbetween resins (see FIG. 2B), thin wall, and any other predictablephenomenon related to the geometry of the object to be printed. Printdata from slicing 184, typically a 2D layer map (e.g. BMP) is thencombined with the pre-print data to form a first data correction filter(DCF 1) 186. Data from the first data correction filter 186 is thencombined with the information providing from real-time measurements ofthe layer thickness and/or a map of distances between the printing blockand printed layer, provided by one or more sensors 200, to form a seconddata correction filter (DCF 2) 202 which is provided to the layer beingprinted. Typically, sensor 200 may include a proximity sensor, a CCD orlinear CCD camera, and/or an accelerometer included in the roller tomeasure “bump” events. Sensor 200 may be used to measure the actualthickness of a printed layer and a comparator compares the result withthe output of the first data correction algorithm filter 186. Datacorrection algorithm filter 202 carries out a transformation of theprint data based on the measured errors so that the printed layer 188 isprinted more smoothly. Movement of the tray is performed and asubsequent layer 190 may be printed.

In some embodiments of the invention, nozzle scattering (movement of theprinthead in Y direction) is made between layers so as to minimize theimpact of missing nozzles. In that case, the movement of the printheadis recorded in order to clearly register the new Y positioning of eachone of the nozzles. This data will be taken into account when updatingthe height map according to the nozzle weighting values of the newprinted layer.

It is expected that during the life of a patent maturing from thisapplication many relevant additive manufacturing and scanningtechnologies will be developed and the scopes of the corresponding termsare intended to include all such new technologies a priori.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting. In addition, any priority document(s) of this applicationis/are hereby incorporated herein by reference in its/their entirety.

What is claimed is:
 1. A method of additive manufacturing a three-dimensional object by layerwise deposition of a building material with an inkjet printing system comprising a print head and a building tray, the printhead comprising a plurality of nozzles, said method comprising: calculating a weighting value for each nozzle of said printhead, said weighting value corresponding to an amount of material being dispensed by each of said nozzles; for each layer of the object being printed: i. obtaining a two-dimensional map of the layer, said two-dimensional map comprising active pixels at (X,Y) positions where building material should be dispensed; ii. obtaining a first Data Correction Filter (DCF1) including a height map of the previous layer which comprises a series of (X,Y) position weighting values, each position weighting value being based on nozzle weighting values and representing the amount of material that has been cumulatively dispensed at each said (X,Y) position in the preceding layers; iii. obtaining a second Data Correction Filter (DCF2) including a thickness map and/or a proximity map of the previous layer; said map(s) being constructed from data obtained from one or more sensors that have scanned said previous layer; iv. comparing the data of the two-dimensional map to the data provided by DCF1 and DCF2 per each (X,Y) position and determining whether a nozzle should be activated at said (X,Y) position to dispense an amount of material; v. printing the layer based on the data obtained in (iv); vi. updating the position weighting values of the height map of DCF1; and vii. adjusting the position of the print head vis a vis the printing tray; repeating steps (i) to (vii) above until the three-dimensional object is printed.
 2. The method of claim 1, wherein the weighting value for each nozzle of the printhead is calculated by: (a) pre-printing an object with a Y length of at least the length of the printhead, said object comprising a plurality of layers so that a print head printing profile can be observed; (b) digitizing said pre-printed object and mapping each one the print head nozzles to said profile; and (c) attributing the weighting value to each nozzle based on said digitized printing profile.
 3. The method of claim 1, wherein the two-dimensional map of the layer of step (i) is provided by a slicer software.
 4. The method of claim 1, wherein the DCF1 of step (ii) is stored in a computer memory.
 5. The method of claim 1, wherein the DCF1 further includes compensation data related to known printing phenomena and/or to the geometry of the three-dimensional object being printed.
 6. The method of claim 1, wherein step (vi) is performed by adding to each (X,Y) position wherein a nozzle has been activated, the weighting value of said nozzle so that the (X,Y) position weighting value is updated.
 7. The method of claim 1, further comprising scanning the printed layer with a sensor and modulating the DCF1 of the next layer with the data collected by said sensor.
 8. The method of claim 7, wherein said sensor is a CCD camera or a linear CCD camera.
 9. The method of claim 7, wherein said sensor is a proximity sensor.
 10. The method of claim 1, further comprising smoothing one or more printed layers with a leveling device selected from a planarizer, a roller and a scraper.
 11. The method of claim 10, wherein said leveling device removes less than 5-10% of the amount of material deposited in said layer. 